U0001 Code: High Speed CAN Communication Bus
A module found the high-speed CAN network itself misbehaving, not just one silent module.
Stop driving
If the engine won't start, the transmission is stuck in one gear or the steering suddenly gets heavy, stop and have the car towed. A history-only U0001 on a car that behaves normally can be driven to a shop, but the fault will usually come back when the damaged wire moves or gets wet.
At a glance
Severity: High
- Meaning
- High Speed CAN Communication Bus
- System
- Module Communication · Network
- Safe to drive?
- With caution
- Typical repair cost
- $75–$1,500
- DIY difficulty
- Hard
U0001 is a bus-level code. The module that stored it judged the whole high-speed CAN network to be faulty: wrong line voltages, missing acknowledgements, or messages from several modules failing at the same moment. This is the fast network (typically 500 kbit/s) that ties the engine, transmission, ABS, steering and instrument cluster together over one twisted pair of wires, with a 120-ohm terminating resistor at each physical end, usually built into two modules. An enhanced scan tool often shows a suffix after the code (for example -88 for bus off); that suffix says more about the fault type than U0001 alone.
How to read U0001
- U Network
- 0 Generic (SAE)
- 0 Module Communication
- 01 Specific fault
Symptoms
- A cluster of warning lights at once: check engine, ABS, stability, steering, transmission
- Gauges drop to zero, the cluster reboots or shows 'service' messages
- Crank-no-start or no-crank because immobilizer data can't cross the bus
- Transmission in limp mode and electric power steering assist cut
- Scan tool lists several high-speed modules as not responding
- Faults that follow rain, a car wash, a bump or opening a door
Possible causes
Ranked by how often each cause is behind this code (editorial estimate).
- CAN-high or CAN-low shorted to ground, to 12 V or to each other (chafed harness, crushed wire, pinched under a trim panel)
- Water in a connector or splice pack on the bus, often from a cowl, sunroof-drain or door-seal leak
- Aftermarket device spliced into the twisted pair (remote start, radio interface, tracker, tuning box)
- Open or missing terminating resistor, e.g. a terminating module unplugged or replaced with the wrong part
- One module with a failed CAN transceiver dragging the bus down
- Severe voltage dip during cranking, jump-starting or charging-system failure
Diagnosis step by step
Scan the whole network and note the suffix
Run a full-vehicle scan, write down which modules answer and which are missing, and record any failure-type suffix on U0001. A single silent branch points to one leg of the wiring; everything silent points to the main trunk or a module shorting the pair.
Tools: OBD-II scanner
Measure bus resistance at the DLC
Disconnect the battery and wait a few minutes, then measure between OBD pins 6 and 14. About 60 ohms is correct; around 120 ohms means one terminator or one end of the bus is open; well under 50 ohms suggests an extra terminator from an add-on or wrong module; near zero is a short between the lines.
Tools: Multimeter
Check each wire to ground and to power
Still with the battery off, pin 6 and pin 14 to chassis ground should read thousands of ohms. With the key on, a DC meter usually shows about 2.6 V on CAN-high and 2.4 V on CAN-low; a line pinned near 0 V or near battery voltage is shorted. A lab scope, if available, shows the mirrored square waves and any noise far better.
Tools: Multimeter
Find the two terminating modules
Use the wiring diagram to identify which modules carry the 120-ohm resistors. Unplug one: the DLC reading should rise to about 120 ohms; if it doesn't change, the fault lies between the DLC and that module.
Tools: Multimeter, Screwdriver
Split the bus and isolate the culprit
With the key on, unplug modules or disconnect branch connectors one at a time while watching line voltages or scan-tool communication. The bus recovering after one module is unplugged identifies the module or its pigtail.
Tools: Multimeter, OBD-II scanner
Inspect wet areas and add-ons
Pull carpet and kick panels near the footwells, check under the battery tray and at the firewall pass-through for green corrosion. Remove any aftermarket module tapped into the CAN wires and restore the factory twist before retesting.
Tools: Flashlight, Pliers
Where the parts are
- 1Battery
- 2Alternator
- 3Engine computer (ECM)
- 4CAN bus
- 5Transmission
- 6Wheel speed sensor
- 7High-voltage battery
Repair options & costs
| Repair | DIY? | Estimated cost |
|---|---|---|
| Network diagnosis (shop labor) | No | $150–$450 |
| Repair chafed or shorted CAN wiring | No | $150–$700 |
| Dry out and replace a corroded connector or splice pack, fix the water leak | No | $200–$800 |
| Remove or properly reinstall an aftermarket device | Yes | $75–$300 |
| Replace a module with a failed CAN transceiver (with programming) | No | $400–$1,500 |
Rough US estimates for parts and labor; shop rates vary by region. Not a quote.
Notes by brand
Field data
| Chrysler | 6 | Pacifica, 200 | |
|---|---|---|---|
| Jeep | 5 | Cherokee, Grand Cherokee Srt, Renegade | |
| Dodge | 2 | Challenger, Durango |
Source: NHTSA Complaints API (US government open data), analyzed by DTC mention.
Emissions / smog test impact
Depends
Whether U0001 fails a US emissions test depends on whether the check engine light is on and whether the station's equipment can read the PCM. A network problem bad enough to block readiness data usually means the vehicle is rejected until repaired.
Frequently asked questions
What is the difference between U0001 and a lost-communication code like U0100?
A lost-communication code names one module that went quiet. U0001 says the bus itself failed its checks, so the fault can be anywhere on the shared pair of wires or in any module connected to it.
Why should the reading across pins 6 and 14 be 60 ohms?
The high-speed bus has a 120-ohm resistor at each end, and two 120-ohm resistors in parallel measure 60 ohms. The reading tells you instantly whether both ends are intact, one is missing, or the lines are shorted.
Can a cheap OBD dongle cause U0001?
It can. A faulty plug-in device or one that keeps talking on the bus can disturb traffic, and badly spliced remote starters are an even more common cause. Unplugging all add-ons is a free first test.
Will replacing the module that logged U0001 fix it?
Rarely. The reporting module is usually the witness, not the culprit. Wiring, water intrusion and add-ons need to be ruled out first.
Sources
- SAE J2012 – Diagnostic Trouble Code Definitions
- ISO 15031-6 – Road vehicles, diagnostic trouble code definitions (EOBD)
- Manufacturer public service information (cross-checked)
- NHTSA Complaints API
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